1. Field of the Invention
The present invention relates to deflection structures for corpuscular beam blanking systems and methods for operating such devices, and in particular to such a deflection structure having two deflection electrodes.
2. Description of the Prior Art
High frequency cut-in and cut-out of an electron beam is required, for example, for stroboscopic electron beam mensuration technology. A deflector capacitor is conventionally employed for beam blanking in electron beam mensuration technology. Such a deflection system is described, for example, in the article "Beam Chopper For Subnanosecond Pulses in Scanning Electron Microscopy," H. P. Feuerbaum et al, J. Phws. E: Sci. Instrum., Volume 11, 1978, pages 529-532. The two deflector plates of the deflector capacitor are conventionally charged simultaneously with pulses, the voltages at the two deflector plates exhibiting opposite operational signs. A pulse generator having two outputs, namely a "+" and a "-" output is required for such a so-called symmetrical circuit for the two deflector plates of the deflector capacitor.
It is technically simpler and more economical to construct a fast pulse generator with only one output, and thus to charge only a single deflector plate of the deflector capacitor with voltage pulses. The second deflector plate in such devices must be then supplied with a chronologically constant voltage. This is conventionally achieved by grounding the second deflector plate. Deflection structures having such a so-called asymmetrical wiring of the deflector capacitor are described, for example, in German patent application No. P3036660.0. Such asymmetrical wiring of the deflector capacitor, wherein one deflector plate is supplied with a chronologically constant potential, effects an energy spread of the corpuscular beam through the pulse deflector field which is higher than in systems employing symmetrical wiring. Such a higher energy spread of the corpuscular beam causes an enlargement of the diameter of the corpuscular beam probe due to the axial color aberration of the lenses which are disposed in the corpuscular beam direction after the corpuscular beam blanking system. The differential transit time effects also increase in direct proportion with an increase in the energy spread of the corpuscular beam, these effects causing a chronological "smear" of the corpuscular pulse in its path to the target. For these reasons, asymmetrical wiring of the deflector capacitor is not practical for obtaining accurate mensuration results.